Fluid exhaust means for hydraulically operated clutches



March 1954 F. R. MOFARLAND FLUID EXHAUST MEANS FOR HYDRAULICALLY OPERATED CLUTCHES Filed Aug. 11, 1950 GUM/M Patented Mar. 2, 1954 FLUID EXHAUST MEANS FOR HYDRAULI- CALLY OPERATED CLUTCHES Forest R. McFarland, Huntington Woods, Mich, assignor to Packard Motor Car Company, Detroit, Mich., a corporation of Michigan Application August 11, 1950, Serial No. 178,975 8 Claims. (01. 192-85) This invention relates to rotatable fluid pressure operated clutches, and particularly to a means for obtaining a complete release of the clutch at high rotative clutch speeds. For purposes of illustration this invention will be described with respect to its application to a speed changing power transmission for automotive vehicles, but it is understood that the invention is not limited to such devices.

It has been proposed to operate a clutch of the friction type by fluid under pressiu'e acting against a piston which compresses the driving and driven members of the clutch together for rotation in unison. In one popular form, the iston is annular in shape and is confined in an annular cylinder secured to either the driving or driven clutch member and rotatable therewith. Under certain circumstances the clutch may be in a released condition while the two members are rotating at high speed due to associated gearing being operated in other driving relationships. If the fluid used to operate the clutch is oil, the release of the clutch is effected by venting the fluid behind the piston and allowing the fluid to escape to the sump. It has been found that despite the venting of the fluid, not all of the fluid escapes from the cylinder, due largely to the fact that it is necessary to vent the cylinder through the shaft which is at a smaller radius than the outermost radius of the cylinder and allows a portion of the fluid to remain in the cylinder and venting passage. The fluid that remains is then rotated at the high speed of the associated clutch member and perforce develops a relatively high pressure head which acts against the piston to engage the clutch.

Thus under conditions described above the clutch may be urged towardthe engaging position even though the operator has conditioned the fluid pressure system for disengagement of the clutch. The resulting damage to the transmission or vehicle or both is readily apparent.

The principal object of this invention is to provide a means for effecting a complete release of a fluid operated clutch using a rotating piston and cylinder as the clutch operating means.

A more specific object of this invention is the provision in a rotating piston of a means for'preventing the undesired creation of a pressure head behind the piston by residual fluid after the operating fluid has been vented.

Yet another specific object of this invention is to provide a means for completely removing the trapped fluid behind a rotatable clutch operating piston to prevent the undesired operation of the clutch, said means including a check valve for automatically admitting air into the space occupied by the fluid, whereby to insure the removal of the fluid.

A further specific object of this invention is to provide a vent valve for afluid-operated multipleplate friction clutch in which one of the plates performs the function of the vent valve.

These and other objects of this invention will become apparent from the following detailed description when taken together with the accompanying drawings in which- Fig. 1 is a section through a change speed transmission utilizing a multiple plate friction clutch and an annular piston for operating the clutch, said piston having a vent valve therein which is constructed in accordance with the teachings of this invention; and

Fig. 2 is a section through an air inlet valve associated with the vent valve shown in Fig. 1.

Referring now to the drawings for a detailed description of the invention there is shown a drive shaft In which is splined to a sun gear Ii of a complex planetary gear set A. Said gear set includes, in addition to the sun gear I I, a plurality of crossed planet gears I3 meshing with sun gear I I, a plurality of planet gears I4 mesh ing with planet gears I3 and a ring gear I5 and a sun gear i6 meshing with planet gears I4. Ring gear I5 is made as a unit with a drum I'I forming the rotatable part of a friction brake B. The stationary part of the brake B is a band I8 operated by any suitable means to contract against the drum I! to arrest the rotation of the drum.

Planet gears I3 and I 4 are mounted on a carrier I9 which is fixed to rotate with an output shaft 20. Thus when brake B is operated, ring gear I5 is held against rotation, and with sun gear II driven by shaft I0, carrier i9 and shaft 20 will be rotated in a reverse direction and reduced speed with respect to shaft I0.

Sun gear I6 is free to rotate on shaft I0 and is formed with a flange 2| to which is splined a drum 22. Said drum 22 forms with a substantially stationary band 23 a second brake designated generally by the reference character C. When brake C is operated, sun gear I6 is held against rotation, thus causing carrier I 9 to rotate in the same direction as, and at a reduced speed with respect to, shaft I0.

Within drum 22 is a multiple plate friction clutch D comprised of a plurality of plates 24 splined to drum 22, and a corresponding plurality of plates 25 disposed between plates 24, each plate 25 being splined to a hub member 26 which, in

3 turn, is splined to shaft 13. Thus the operation of clutch D couples sun gear [8 to shaft 10, and since gear H is splined to shaft ill, the operation of clutch D locks the two sun gears together and establishes a direct drive between shaft i9 and output shaft 29.

Drum 22 is a hollow annulus having in addition to the part contacted by band 23, an inner cylindrical part 21 and a radially disposed part 28. Thus drum 22 and the parts 21 and 28 thereof form an annular cylinder. Within the said cylinder is located a piston 29- having a.si irt.3ll' and an outer flange 31, the latter serving as the pressure transmitting means. for the piston 29. A spring 32 encircles skirt 3!! and. is, retained in compression between piston 29 and an abutment 33 on cylindrical part 21. Spring 32. therefore serves to urge piston 29 to the left as viewed in Fig. 1, that is, it urges piston 29 into the, annular cylinder. The space 34 in the cylinder is adapted to be filled with fluid under pressure through one or more bores'35 in cylindrical'part 21- aligned with a peripheral groove 36 communicating with a passageway 31 connected through-- another passageway 33, to a check valve 39 andto a source of fluid under pressure (not shown). It is contemplated that the fluid will be controlled by suitable valves such as those disclosed in my copending application Serial'No. 71,128, flledJanuary 15., 1949, so that when it is desired to cperate. clutch D, fluid under pressure will be ad mitted to space 34 tourge'piston 29 to the right as viewed in Fig. 1;.to compress plates-24 and 25 against flange 2i, and when it is desired to release clutch D, thefluid space:34w ill,be vented and spring 32 will move piston; 29v to the left as viewed in Fig. 1. as aforesaidto allow plates 24. and 25 to separate.

It will be noted that even when released, clutch D, and particularly the fluid. in space 3.4 will be: rotated at the speedof sun gear 1:3, and hence any fluid remaining-in saidispace will be rotated) likewise and will develop a pressure head. which; increases asv the square of. the velocity. Thispressure head may becomehigh enough to overcome the resistance of spring 3.2: and operate; clutch D, even though space. 34. may. be vented. Such undesired operation of; the;- clutch; is oft course to be avoided.

The means used to, avoid the building; up at pressure in space 34, when clutchD-is' to be. released comprises one or moreybleed;openings-40 in outer flange 3i. connecting space 34 with re. cesses 41 in which are disposed springs 42 comepressed between the bottom: of the. said recesses 4| and the first plate 4.3 of the plurality of plates 24 splined to drum 22. Bleed; openings to are; smaller in cross sectionalareathamthe'area of the bores so that whenfluid under-pressure is admitted to space. 34 it cannot-escape through; bleed openings as fast-as the fluidenters space: 34. The presence of bleed openings; therefore cannot prevent movement of piston 29 to the; right as viewed in Fig. 1 againstgthe resistance;- of spring 32. Continued movement of Piston 29 in this direction compresses the'twosetsof plates;

24 and 25 together and against flange 2i; and by this action plate 43 will beheld firmly against. recesses 41 to prevent escape of fluid under pres--:

sure from chamber 34. Plate 43, thus; functions:

as aplate valve forbleed openings 40.

When clutch D is released, spring 32 will; re tum piston 29 to its left-hand positionr(Eig; l) .1

andpermit a separation oftheplates 24 andifi Springs 42 will thenpush plate: 43 away from: r

piston 29 and specifically away from recesses 41, thereby theoretically allowing residual fluid in space 34 to escape through bleed openings 49 and the recesses 41. If all of the residual operating fluid in space 34 is removed, the undesired building up of pressure due to rotation of drum 22- will beavoided andaclutch D will be released as desired.

It has been found that providing an opening such as 49 for the escape of trapped fluid is not always suflicient, to. prevent the undesirable accumulation of. fluid in space 34. The escaping fluid" must be replaced with air, otherwise an unbalanced pressure. system is produced in the fluid: flow: passages. as explained below, which tends to. produce a reduced pressure behind the fluid. flowing from space 34, which of course would retard the removal of such fluid. Under certain circumstances, the unbalance in pressure might be so great as to produce a circulation of fluidfrom the fluid supply and vent lines forming a part of the controls, through the passages 39; and 31, and space 34 to maintain the space fullE even though the clutch should be released. It is. therefore desirable to vent the pressure line between chamber 34 and the controls in order to admit air through theline and into chamber 34 to replace the oil with air-asrapidly as possible. This can be done by av common type of ball check valve, one form of which is shown in this disclosure. Check valve 39 isprovided in passageway 38 which is'in hydraulic communication withspace 34, said valve 39 being designed to open. a port 44 by means of; a'ball 45 retained in an;

opening 46 by-a cross-shaped plug 41 shown in cross section in Fig; 2.- When the controls are. operative to causethe pressure to fall within. passage 38, the check valve 390pens and air can pass through opening 44' through the channeled. sides 48 of the plug 47 and into passage 38. It will be noted that bleed openings 49 are locatedat as great a radius as ispossible so that nearlyall of the fluid in space 34' can be drained out of. the said space'by centrifugal force. The fluid in peripheral groove 35 and passagewaystfl and33': will thus, be at subatmospheric; pressure due, to this centrifugal pumping action and contrari-- wise the pressure ofithez-fluid in: bleed openings; 49 will be at higher than atmosphericypressurez .This:subatmospheridpressure causes ball 45'to:

" be drawn to the left, as viewed in Fig. 1, to un cover port 44 to admitair to take the place 01:- the fluid escaping through, bleed openings 49,. thereby'hastening-the removallof the fluid from.

1 space 34.

When clutch D is operated, opening 46 isfllled with fluid under clutch operating pressure through passageways 31' and 33 and will hold ball 45 against opening 44 to close the checkvalve'39.

The'use of a. check valve suches 39 renders the successful operation of the emptying means independentof any valving that may be used to control the operation of the clutch D. Were it not for check valve 39,,a corresponding function would have. to be performed by theval'ving. and this might not be convenient or desirable. from. the standpoint of thefunctioning of. the transmission: as awhole.

It is understood that the foregoing description. is 'merely illustrative of a preferred embodiment of the invention andthati the scope of this, in--. ventionis not, to be: limited thereto but: is.,to;be;

determined bye-the; appended; claims.

What is claimed is:

1. In combination, a rotatable cylinder, a piston in th cylinder, a coupling operated by the piston, means for introducing fluid under pressure into the cylinder to operate the coupling, said pressure being releasable to render the cow pling inoperative, and means for substantially emptying the cylinder of residual fluid when the pressure is released, said last-named means comprising a bleed opening in the piston, means for closing the bleed opening upon partial operation of the coupling, and a pressure differential operated valve in communication with the pressure fluid on one side and with atmospheric pressure on the other, said valve being adapted to admit air into the fluid introducing means when the fluid pressure falls below atmospheric.

2. In combination, a rotatable cylinder, a piston in the cylinder, a multiple plate friction clutch operated by the piston, means for introducing fluid under pressure into the cylinder to operate the clutch, said pressure being releasable to render the clutch inoperative, and means for substantially emptying the cylinder of residual fluid, said last-named means comprising a bleed opening in the piston adjacent one of the plates of the clutch and adapted to be closed by said plate upon partial operation of the clutch, resilient means interposed between the piston and the said adjacent plate to prevent the closing of said bleed opening except upon the introduction of fluid under pressure into the cylinder, and a pressure differential operated valve in communication with the pressure fluid on one side and with atmospheric pressure on the other, said valve being adapted to admit air into the fluid introducing means when the fluid pressure falls below atmospheric.

3. In combination, a rotatable cylinder, a piston in the cylinder, a friction clutch operated by the piston, said clutch including a movable plate, means for introducing fluid under pressure into the cylinder to operate the clutch, said pressure being releasable to render the clutch inoperative, and means for substantially emptying the cylinder of residual fluid, said last-named means comprising a bleed opening in the cylinder terminating in proximity to the clutch plate, said opening being enlarged at the clutch plate, a spring in the enlarged opening urging the plate away from the opening, said bleed opening allowing less fluid to pass therethrough than is admitted by the means for introducing fluid under pressure into the cylinder, such that the piston is moved against the clutch plate to close the bleed opening despite the force of the spring tending to separate the piston and plate, and means for replacing the residual fluid in the cylinder with air after the fluid pressure in the cylinder is released.

4. The combination described in claim 3, said means for replacing the residual fluid in the cylinder with air comprising a check valve in communication with the cylinder and with the atmosphere and adapted to open the cylinder to atmospheric pressure when the pressure in the cylinder becomes less than atmospheric.

5. In combination, a rotatable cylinder, a piston in the cylinder, a coupling operated by the piston, means for introducing fluid under pressure into the cylinder to operate the coupling, said pressure being releasable to render the coupling inoperative, and means for substantially emptying the cylinder of residual fluid when the pressure is released, said last-named means com prising a bleed opening in the piston, means for closing the bleed opening upon partial operation of the coupling, and a non-rotating pressure differential operated valve in fluid communication with the cylinder and with the atmosphere and adapted to admit air into the cylinder when the pressure in the cylinder falls below atmospheric pressure and to close when the pressure in the cylinder exceeds atmospheric pressure.

6. The combination described in claim 5, said non-rotating pressure differential operated valve comprising a ball check valve.

7. The combination described in claim 5, said non-rotating pressure difierential operated valve comprising a ball check valve, and means for limiting movement of the valve in response to atmospheric pressure, said movement limiting means comprising a plug in the fluid communicating with the cylinder, said plug having an abutment adapted to contact the ball at substantially one point and a passage spaced from the abutment to allow fluid to pass through the plug to and from the cylinder.

8. The combination described in claim 5, said non-rotating pressure diiferential operated valve comprising a ball check valve, and means for limiting movement of the valve in response to atmospheric pressure, said movement limiting means comprising a plug in the fluid communicating with the cylinder, said plug having a crossshaped section normal to the flow of fluid therethrough and a plane surface at the end thereof adjacent the ball such that when the ball contacts the plug at the plane-surfaced end thereof under the influence of atmospheric pressure, said ball will permit the passage of air through the plug.

FOREST R. MCFARLAND.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,934,850 Fromaget Nov. 14, 1933 2,143,321 Kegresse Jan. 10, 1939 2,170,538 Sarver Aug. 22, 1939 2,386,217 Kegresse Oct. 9, 1945 2,386,220 Lawler et a1 Oct. '9, 1945 2,495,988 Sheppard Jan. 31, 1950 2,583,919 Wilson Jan. 29, 1952 FOREIGN PATENTS Number Country Date 109,420 Sweden Dec. 28, 1943 684,091 Germany Nov. 22, 1939 

